Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$125.74	8.627%	$136.5876	$136.59	$136.60	$136.60
Purchase #2	$200.51	5.661%	$211.8609	$211.86	$211.85	$211.90
Purchase #3	$97.85	12.858%	$110.4316	$110.43	$110.45	$110.40
Purchase #4	$155.69	6.403%	$165.6588	$165.66	$165.65	$165.70
Purchase #5	$77.29	3.182%	$79.7494	$79.75	$79.75	$79.70
Purchase #6	$70.61	11.133%	$78.471	$78.47	$78.45	$78.50
Purchase #7	$184.32	3.676%	$191.0956	$191.10	$191.10	$191.10
7 purchase totals =	$912.01		$973.8549	$973.86	$973.85	$973.90